Many devices used in electronics or industrial machinery include elements which generate or absorb heat locally. Usually, such devices are provided with means for radiating heat to avoid overheating of a heat-generating element or to avoid excessive cooling of a heat-absorbing element, which condition may cause, for example, a malfunctioning of or a damage to the heat-generating element or heat-absorbing element (such an element is hereinafter referred to as "heat-generating element" collectively) itself or other components located nearby.
For example, a personal computer includes many heat-generating elements such as a CPU (MPU), memory modules, and a hard disk drive. To ensure stable operation, heat generated by these elements is transferred to the housing or the keyboard by conduction and radiated into the air naturally (hereinafter referred to as "natural air-cooling") or cooled by a small fan (hereinafter referred to as "forced air-cooling").
In recent years, microprocessors have gone through a number of drastic performance improvements and modularization. Because of this advancement, the rate of heat generated when they operate has increased accordingly. Notebook type personal computers which include such microprocessors in highly miniaturized thin bodies are now pushed to a limit in the design of heat conduction and radiation because they are designed to utilize natural air-cooling or forced-air cooling for dispersing the heat generated by the microprocessors, etc.
In this situation, heat transportation type cooling devices are now coming into practical use. A cooling device of this type includes heat-collecting means which comprises a metal plate, and the heat-collecting means is adhered to a heat-generating element. The heat from the heat-generating element is absorbed by this heat-collecting means and is transferred through heat-transferring means such as a heat pipe to the external part of the main body of the computer, where the heat is radiated by heat-radiating means, which may comprise a heat-radiating fin or a cooling fan provided externally on the computer. It is known that such heat-transferring means provides a high efficiency for the cooling of the heat-generating element. In addition, because the heat-radiating fin and the cooling fan are arranged externally over the computer, the internal space of the computer can be designed more effectively for further miniaturization, or the degree of freedom in component arrangement is improved.
By the way, there is a notebook book type personal computer (hereinafter referred to as "note PC") in which a floppy disk drive (hereinafter referred to as "FD drive") and a CD-ROM drive (hereinafter referred to as "CD drive") are provided not in the main body of the note PC but are in a separate station for improved portability and for battery power conservation. In this case, because the main body of the note PC is separable from the station and independently portable, the note PC can be further reduced in thickness and weight for a portability improvement. To enable the operation of the note PC in this separated condition, a built-in battery is provided in the main body, and generally the operational speed of the built-in microprocessor is reduced to conserve energy and increase the life of the battery.
When this thin note PC is mounted on the station, the note PC receives power through a power adapter from a home-use power supply. In this condition, the microprocessor can access to all the drives in the station and operates at a full speed without any influence from the condition of the battery.
When this separable thin note PC is used separately from the station as a portable unit, the microprocessor is controlled to operate at a speed which is restricted for power conservation. Therefore, the microprocessor produces heat at a rate lower than when it is operated at a full speed on the station. Although the rate of the heat produced by the microprocessor is lower when the note PC is used separately than when it is used with the station, the cooling device of the note PC must be designed to have a capacity sufficient for cooling the microprocessor that is operated at a full speed. This design condition requires a comparatively large cooling device and makes it difficult for the main body of the note PC to be miniaturized further.